PROJECT SUMMARY Alzheimer's disease (AD) is the most common form of dementia and is characterized by pathological lesions including deposition of amyloid plaques in parenchyma and cerebral vasculature (cerebral amyloid angiopathy, CAA), neurofibrillary tangles, and neuroinflammation. AD severely affects the quality of life of the patients and is the sixth leading cause of death in the United States. Uncovering novel mechanisms that control AD pathogenesis may advance development of more effective therapeutics to treat this devastating disease. Heparan sulfate (HS), a type of polysaccharide, is an essential component of the cell microenvironment and plays an important role in cell-cell and cell-matrix interaction and signaling. HS is elevated in human and mouse AD brains and co-deposits with amyloid-?(A?) in parenchyma and cerebral vasculature. Recent genetic studies determined that neuronal HS facilitates A? oligomerization and deposition in AD mouse models. Currently, it is remains unknown what causes the aberrant HS expression, and, more importantly, what are the functional consequences of the aberrant HS expression in AD pathogenesis. In this application, we propose to test our novel hypothesis ?Hypoxia induces aberrant HS expression in brain endothelial cells and macrophage/microglia, creating pathogenic cellular environments that exacerbate A? pathology in vasculature and neuroinflammation to aggravate CAA/AD pathogenesis? by pursuing the following three Specific Aims: 1. Map cell-type specific HS expression in AD brain and determine if aberrant HS expression correlates with hypoxia and AD onset and progression; 2. Determine the roles and related structure of brain endothelial HS in hypoxia-exacerbated CAA/AD pathogenesis; 3. Determine the roles of macrophage/microglia HS in hypoxia-exacerbated AD pathogenesis. The proposed studies will use both novel and established genetic, cellular, RNAseq, biochemical and bioinformatics approaches in conjunction with in vitro cell function and in vivo mouse models. These serial investigations are anticipated to delineate a novel mechanism that drives aberrant HS expression in AD, reveal the aberrant HS expression to be a novel biomarker for AD early diagnosis and prognosis, and elucidate the pivotal roles and their underlying cellular and molecular mechanisms of the aberrant HS expression in AD pathogenesis, which likely will contribute to the development of novel therapeutics for AD treatment. 1